1. Field of the Invention
The present invention relates to an image forming system, and more particularly, to an image transfer control, in a multiply-connecting image forming system capable of subjecting a recording material having an image formed thereon by a first image forming apparatus to image formation by a second image forming apparatus, for the second image forming apparatus in a case where only the second image forming apparatus continues image formation.
2. Description of the Related Art
There is widely used an image forming apparatus in which a toner image forming portion forms a toner image and transfers the toner image onto a recording material, and then a fixing portion heats and pressurizes the recording material to fix the image onto the recording material. Further, there is widely used an image forming apparatus capable of performing duplex printing, including a reverse conveyance mechanism configured so that the recording material having an image formed thereon by the toner image forming portion and the fixing portion is sent again to the same toner image forming portion in a state in which a front surface and a back surface of the recording material are reversed.
In Japanese Patent Application Laid-Open No. 2006-58881, there is proposed a multiply-connecting image forming system constructed by connecting, through intermediation of a conveyance path, two image forming apparatus, that is, a first image forming apparatus and a second image forming apparatus, which each include the reverse conveyance mechanism and are capable of solely performing duplex printing. In this case, the conveyance path is provided with a switchback reverse conveyance mechanism for a recording material, to thereby deliver the recording material from the first image forming apparatus to the second image forming apparatus in a state in which a leading edge and a trailing edge of the recording material are reversed.
The individual image forming apparatus successively perform front surface printing and back surface printing in a divided manner, to thereby greatly increase printing speed as compared to a case where a single image forming apparatus is used to perform duplex printing with use of its reverse conveyance mechanism.
In the multiply-connecting image forming system described above, a large capacity recording material deck is, in many cases, arranged on an upstream side of the two image forming apparatus. In a case where the image forming apparatus on the upstream side has run out of toner during duplex image formation using the large capacity recording material deck, it is conceived that the recording material is caused to pass through the image forming apparatus on the upstream side to continue the duplex image formation using only the image forming apparatus on the downstream side without performing image formation by the image forming apparatus on the upstream side.
In this case, however, the recording material, which has passed through the fixing device at the fixing temperature one time, is reduced in amount of water contained therein. Therefore, the image forming apparatus on the downstream side needs to be set in an appropriate transfer condition, which may otherwise lead to degradation in quality of an output image obtained through the image formation on the downstream side.